133 



at temperatures rarely below 70. The earliest record in channel 

 waters was on May 1, 1896, at 68.75, and the latest on November 

 15, 1897, at 47. Of the 28 records in channel waters the months 

 from May to September have, respectively, 6, 3, 10, 7, and 1 record, 

 and there is 1 in November. Hydra is thus a late vernal and a 

 summer planktont in our waters. 



Observations in the field and a cursory examination of the col- 

 lections made in the backwaters have indicated that Hydra is often 

 very abundant on the vegetation. It is also limnejtic in habit, 

 floating with the foot attached to the surface film and tentacles 

 widely extended; or, without attachment, in the deeper strata of 

 water. A similar limnetic habit was often observed in the case of 

 Hydra in channel waters, especially on still warm days when the 

 surface was unruffled. 



Hydra \vas generally more abundant in the plankton in May or 

 in early summer. The maximum record in channel waters was 

 3,200 per m. 3 on July 21, 1897, the error of dilution being, however, 

 large in this record. In Quiver Lake on May 8, 1896, a maximum 

 record of 5,335 per m. 3 was made, the error of dilution being very 

 small. This was during a vernal plankton pulse (8.14 cm. 3 per m. 3 ) 

 in these waters, when the food of Hydra was present in considerable 

 abundance. 



Hydra viridis L. was seen 'frequently in spring-fed backwaters 

 and in laboratory aquaria, but was never recognized in plankton 

 collections made in channel or backwaters. The limnetic habit 

 noted in H. fusca was not observed in the case of this species. . 



PLATYHELMINTHES. 

 TURBELLARIA. 



Numerically and from the volumetric standpoint the Turbellana 

 are not of great significance in the plankton of fresh waters as a rule. 

 However, in some seasons and under certain conditions Stenostoma 

 becomes very abundant, as, for example, in autumn months in back- 

 waters, and generally where decaying vegetation abounds. In the 

 autumn of 1895 the plankton in the relict pools of Flag Lake consisted 

 almost entirely of Synura uvella, Stenostoma leucops, and Entomos- 

 traca. 



